JPH10180865A - Manufacture of polyolefin molded object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a polyolefin molded object having high strength and the high modulus of elasticity without requiring a flowability modifier removing process. SOLUTION: This molded object is obtained by melting a compsn. based on 100 pts.wt. of high density polyolefin such as high density polyethylene and 1-30 pts.wt. of a polymerizable monomer or oligomer having compatibility with respect to high density polyolefin and molding the same into a sheet or film to roll and stretch the sheet or film. Thereafter, the polymerizable monomer or oligomer in the sheet or film is polymerized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyolefin molded article having a high strength and a high elastic modulus.

[0002]

2. Description of the Related Art As a method for producing a polyolefin having a high strength and a high elastic modulus, JP-A-1-280013 discloses an ultrahigh molecular weight polyethylene and a flow improver such as paraffin wax. A method is disclosed in which melt-kneading is performed at a temperature not lower than the melting point, extrusion molding is performed from a die, and a molded product is stretched in multiple stages. The publication states that
It is described that an ultrahigh molecular weight polyethylene having high strength and high elastic modulus can be produced on an industrial scale with good productivity and operability by such a method.

[0003]

However, in the method disclosed in the above-mentioned publication, it is necessary to remove the fluidity improver in the molded body by using a solvent during or after the stretching step. There is a problem that a long time is required and a solvent is required to remove the fluidity improver, thereby increasing the production cost.

An object of the present invention is to provide a production method capable of efficiently producing a polyolefin molded article having a high strength and a high elastic modulus without requiring a step of removing a fluidity improving agent or the like.

[0005]

According to the present invention, as described in claim 1, 100 parts by weight of a high-density polyolefin and 1 to 30 parts by weight of a polymerizable unsaturated compound having an affinity for the high-density polyolefin. Melting the composition containing as a main component, forming a sheet or film, rolling the obtained sheet or film, stretching the rolled sheet or film, and the stretched sheet or And a step of polymerizing a polymerizable unsaturated compound in the film.

In the method for producing a polyolefin molded article according to the present invention, preferably, as described in claim 2, a high molecular weight polyolefin is used as the high-density polyolefin.

[0007] In a specific aspect of the present invention, as described in claim 3, the composition further contains a radical generator. Preferably, as described in claim 4,
A photopolymerization initiator is used as the radical generator, and the step of polymerizing the polymerizable unsaturated compound after stretching is performed by ultraviolet irradiation.

However, the step of polymerizing the polymerizable unsaturated compound may be carried out by irradiating with an electron beam. In a specific aspect of the present invention, at least a part of the polymerizable unsaturated compound is a trifunctional compound as described in claim 6.

In the method for producing a polyolefin molded article according to the present invention, preferably, in the step of rolling the sheet or film, the rolling is performed at a rolling ratio of 2 to 10 times. Will be

Preferably, in the step of stretching the sheet or film, the sheet or film is stretched to a stretching ratio of 2 or more. In a more limited aspect of the present invention, as described in claim 9, the high-density polyolefin has a weight average molecular weight of 200,000 to 200,000.
High density polyethylene in the range of 500,000 is used.

When high-density polyethylene is used as the high-density polyolefin, preferably, in the rolling step, rolling is performed at a temperature in the range of 70 to 120 ° C. Preferably, in the stretching step, the stretching is performed in a temperature range from 70 ° C. to the melting point of the high-density polyethylene.

[0012] The method for producing a polyolefin molded article according to the present invention preferably further comprises a step of heat-treating the sheet or film at least before stretching.

[0013] According to a thirteenth aspect of the present invention, the stretching step comprises a multi-stage stretching step of stretching two or more times in the same direction as the rolling direction. A final stretching step of stretching in the same direction at a temperature of 35 ° C. or lower than the stretching temperature and 5 ° C. or lower than the stretching temperature may be performed.

Hereinafter, the present invention will be described in detail. The high-density polyolefin resin used in the present invention is not particularly limited as long as it has high crystallinity. Homopolymers such as polyethylene, polypropylene, 1-butene, and 1-pentene, for example, vinyl acetate, vinyl Copolymers containing 10% by weight or less of a copolymer component such as alcohol, vinyl chloride, and a vinyl monomer such as acrylic acid can be used.

Most preferably, as the high-density polyolefin resin, a high-molecular-weight high-density polyolefin having a large weight-average molecular weight is preferably used because it can enhance mechanical properties such as strength and elastic modulus of the obtained polyolefin molded article. . Here, the high molecular weight polyolefin is
Like the high-density high-molecular-weight polyethylene described below, the weight-average molecular weight is somewhat large, and refers to those that can enhance mechanical properties such as strength and elastic modulus.The weight-average molecular weight varies depending on the type of polyolefin, 20
There are more than ten thousand.

In the present invention, among the above resins, a high density polyethylene resin is preferably used. As a high-density polyethylene resin, its weight average molecular weight is 200,000-
Those in the range of 500,000 are preferably used. When the weight average molecular weight is less than 200,000, the strength and the elastic modulus may not be significantly improved even when the molecular chains are oriented by stretching. When the weight average molecular weight exceeds 500,000, melt molding may not be performed, as typified by ultrahigh molecular weight polyethylene. Therefore, by using a high-density high-molecular-weight polyethylene having a weight-average molecular weight in the range of 200,000 to 500,000 as described above, mechanical properties such as strength and elastic modulus can be further improved as compared with low-molecular-weight polyethylene. .

When a high-density polyethylene resin is used, its density is preferably 0.94 g / cm ³ or more. If the density is low, improvement in strength and elastic modulus may not be expected even after stretching. Further, the melt index (MI) is 0.1-20, more preferably 0.1-10.
Is preferred. When the melt index is smaller than 0.1, a load is imposed on a molding machine such as an extruder, and when it is larger than 20, molding may be difficult.

In the present invention, a composition prepared by mixing 1 to 30 parts by weight of a polymerizable unsaturated compound having an affinity for the high-density polyolefin with respect to 100 parts by weight of the high-density polyolefin is used as a raw material. If the amount of the polymerizable unsaturated compound is less than 1 part by weight, the effect of improving the stretchability by mixing the polymerizable unsaturated compound cannot be expected so much. If the amount exceeds 30 parts by weight, the surface of the molded article will have no polymerizable unsaturated compound. Not only does the saturated compound bleed and the handling properties deteriorate, but also the stretching properties deteriorate.

Hereinafter, the case where a high-density polyethylene resin is used as the high-density polyolefin in the present invention will be described in detail as a typical example. However, when another polyolefin is used, a polyolefin molded article is produced in the same manner as described below. Can be.

The polymerizable unsaturated compound having an affinity for the high-density polyethylene resin is not particularly limited as long as it is a low-molecular-weight unsaturated compound which easily dissolves in the high-density polyethylene resin. And / or polymerizable oligomers can be used. Examples of such a polymerizable monomer and a polymerizable oligomer include various acrylic monomers and oligomers, various vinyl monomers and oligomers, and the like.

Specifically, as the polymerizable monomer, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, diallyl phthalate, triallyl isocyanurate, hexanediol diacrylate, dipentaerythritol pentaacrylate,
Isobonyl acrylate, 2-phenoxy ether acrylate and the like can be mentioned.

Examples of the polymerizable oligomer include epoxy acrylate, urethane acrylate, polyester acrylate, silicone acrylate, and other special oligomers such as liquid butadiene.

As the polymerizable unsaturated compound, trifunctional compounds such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate and triallyl isocyanurate have high reactivity, and the polymer bleeds out to the surface after stretching. Since it is difficult, it is particularly preferably used.

In the present invention, in order to promote the polymerization of the polymerizable monomers and oligomers, it is preferable to add a radical generator represented by various organic peroxides and various photopolymerization initiators. The amount is preferably 3 to 5 parts by weight based on 100 parts by weight of the polymerizable unsaturated compound. Specific examples of the organic peroxide include ditertiary butyl peroxide, dicumyl peroxide, tertiary butyl cumyl peroxide, and the like. Specific examples of the photopolymerization initiator include acetophenone, benzophenone, thioxanthone, benzoin, Michler's ketone, and the like.

As a method of mixing a radical generator into a sheet or film as a molded article, in the case of a photopolymerization initiator, a high-density polyethylene resin, a polymerizable unsaturated compound, a photopolymerization initiator and The composition mixed with
A method of melting and kneading in an extruder at the time of molding is exemplified.
In the case of an organic peroxide, a molded article kneaded with a high-density polyethylene and a polymerizable unsaturated compound may be impregnated into the molded article by placing the molded article in a solvent in which the organic peroxide is dissolved. . Of the above radical generators, a photopolymerization initiator is particularly preferred because of easy mixing and easy handling, and among them, benzophenone and thioxanthone are particularly preferably used.

When the above composition is melt-molded by an extruder or the like, the melting temperature is preferably 130 ° C. or higher, more preferably 140 ° C. or higher. If the melting temperature is lower than 130 ° C., the melting of the resin may be incomplete, the compatibility with the polymerizable unsaturated compound may be reduced, and the stretchability in the subsequent stretching step may be deteriorated. If the melting temperature is too high, the high-density polyethylene resin and the photopolymerization initiator may decompose or evaporate. Therefore, the melting temperature is preferably substantially 250 ° C. or less.

In the present invention, when high-density high-molecular-weight polyethylene is used, mechanical properties such as strength and elastic modulus can be further improved as compared with low-molecular-weight polyethylene. When high molecular weight polyethylene is used, the weight average molecular weight is preferably 2 × 10 ⁵ or more. If the weight average molecular weight is smaller than this, there is a tendency that the strength and the elastic modulus are not significantly improved even when the molecular chains are oriented by stretching. On the other hand, if the molecular weight is too large, melt molding becomes impossible, as typified by ultrahigh molecular weight polyethylene. Therefore, the weight average molecular weight is substantially 5 ×
It is preferably 10 ⁵ or less.

In the present invention, the composition melted by the above method is first formed into a sheet or film.
The forming method is not particularly limited, and a usual roll forming method, calendar forming method, or the like can be used. The initial thickness of the compact greatly affects the subsequent rolling process. That is, the force required for the rolling roll to crush the compact,
Since the so-called rolling force increases as the thickness of the formed body increases, the deflection of the rolling roll increases, and uniform rolling in the width direction cannot be performed. Conversely, if the thickness of the compact is too small, not only the thickness of the compact after rolling is too small, but also the rolling rolls may come into contact with each other and shorten the life of the rolls. Therefore, the thickness of the molded body is 0.5 to
A range of 4 mm is preferred.

In the present invention, heat treatment may be performed before rolling or stretching the sheet or film formed as described above. By subjecting the sheet or film to heat treatment, the crystalline state can be adjusted, the subsequent stretching can be performed smoothly, and the degree of orientation can be improved, which is preferable.

The heat treatment method is not particularly limited, but is desirably performed in a closed vessel under a pressurized condition in order to prevent evaporation of the polymerizable unsaturated compound kneaded in the sheet.

In the present invention, the sheet or film formed as described above is rolled. The rolling method is a commonly performed method, that is, the clearance of a pair of rolling rolls rotating in opposite directions is made smaller than the thickness of the compact, and the compact is inserted between the rolling rolls. This is performed by reducing the thickness and elongating the molded body. If the temperature of the rolling roll in the rolling step is too low, uniform rolling may be difficult due to a large rolling force. On the other hand, if it is too high, the molded body may melt and break during rolling. Therefore, the temperature of the rolling roll in the rolling step is preferably from 70 to 120 ° C, more preferably from 90 to 115 ° C. On the other hand, when the rolling ratio is too low, not only the effect of the rolling cannot be expected, but also the burden on the subsequent stretching step. Conversely, if the rolling ratio is too large, the rolling force increases, and not only uniform rolling becomes difficult, but also the thickness of the molded body becomes too thin, and the molded body may be cut during the subsequent stretching step. . Therefore, the rolling ratio is preferably 2 to 10 times. Here, the rolling ratio is defined by the following equation. (Rolling ratio) = (Thickness of molded body before rolling) / (Thickness of molded body after rolling)

In the present invention, the sheet or film rolled as described above is stretched. The stretching method is not particularly limited, and a usual roll stretching method or zone stretching method can be used. The roll stretching method is a method in which a sheet is sandwiched between at least a pair of rolls having different speeds, and the sheet is pulled while being heated, and is a method in which a molecular chain can be strongly oriented only in a uniaxial direction. In this case, the speed ratio of the pair of rolls becomes the stretching ratio. Zone stretching means that the sheet is locally stretched by locally heating the sheet with a heater or hot air, so that thermal degradation of the sheet during stretching is suppressed, and the reduction in the sheet width direction is small and It has advantages such as enabling uniform stretching.

In the present invention, a roll stretching method which does not require a special device, easily controls the stretching ratio, and has high productivity is preferably used. The method of heating the molded body at this time includes hot air heating, hot water heating, infrared heating, microwave heating, and the like. Among them, hot air heating, which has a simple apparatus and easy temperature control, is preferably used. The number of times of stretching is not particularly limited, but a multi-stage stretching method in which stretching at a low stretching ratio is performed a plurality of times has few stretching breaks and stable stretching is possible. However, when the number of stretching is increased, the stability is increased and the stretching ratio is also increased, but on the other hand, the size of the apparatus is increased. Therefore, the number of stretching is preferably substantially 2 to 5 times.

The stretching temperature ranges from 70 ° C. to the melting point of the high-density polyethylene used, more preferably 80 ° C.
It is in the range of not less than 10 ° C and not more than 10 ° C lower than the melting point of high-density polyethylene. Here, the melting point refers to the maximum point of an endothermic peak accompanying melting of a crystal, which is observed when performing a thermal analysis with a differential scanning calorimeter (DSC) or the like. 70
If the film is stretched at a temperature of not more than ℃, the molded article may be whitened. If the temperature is higher than the melting point, the effect of improving the strength by stretching is not obtained so much, and the molded article may be stretched and cut.

The stretching ratio in the stretching step is preferably 2 times or more, more preferably 3 to 10 times. If the stretching ratio is less than 2, the strength and elastic modulus of the molded article may not be improved. Conversely, if the stretching ratio is too large, the molded product may be easily cut during stretching, so care must be taken. Here, the stretching ratio is defined by the following equation. (Stretch magnification) = (Cross-sectional area of molded article before stretching) / (Cross-sectional area of molded article after stretching)

As described above, the stretching temperature is set at 70
Although it is desirable to be in the range of from ° C. to the melting point of the high-density polyethylene, the stretching temperature in the case of performing the above-described multi-stage stretching, in the multi-stage stretching step of stretching twice or more in the same direction as the rolling direction, the final stretching step When the film is stretched in the same direction at a temperature of 35 ° C. lower than the stretching temperature of the immediately preceding stretching step and at a temperature of 5 ° C. lower than the stretching temperature, it may be desirable in the following points. That is, when the stretching temperature in the final stretching step is reduced as described above,
In some cases, fine voids can be forcibly and stably generated in the sheet, and the sheet can be reduced in weight.

In this case, the stretching temperature in the final stretching step is 5 ° C. lower than the stretching temperature immediately before in the multi-stage stretching step.
If the temperature is lower than the low temperature, fine voids cannot be generated stably, the weight of the sheet may not be sufficiently reduced, and voids may be generated non-uniformly. Uniformity may decrease. Further, when the stretching temperature in the final stretching step is still lower than the temperature 35 ° C. lower than the stretching temperature immediately before in the multi-stage stretching step, the temperature becomes too low, and the final stretching step may not be carried out smoothly.

The sheet in which the fine voids have occurred is usually in a stable whitened state. Conversely, when it is not desired to generate voids in the sheet, the sheet may be rolled again immediately after the final stretching to remove voids.

In the present invention, the polymerization is carried out without removing the polymerizable unsaturated compound in the stretched sheet or film. The polymerization can eliminate a very time-consuming removal step, so that productivity can be greatly improved. As a method of polymerizing the polymerizable unsaturated compound, a method of polymerizing by heating, a method of irradiating ultraviolet rays, a method of irradiating electron beams, and the like can be used, and a method of irradiating ultraviolet rays is most preferably used. In the method by heating, the compact shrinks due to heat,
There is a possibility that the effect of improving the physical properties due to the stretching may be reduced, and in the worst case, the molded body may be melted. In addition, the method using an electron beam requires an expensive device, so that the initial cost is increased and the price of the molded body is increased. When ultraviolet rays are used, it is preferable to mix the above-mentioned photopolymerization initiator in the molded article in order to promote polymerization.

(Function) In the present invention, a polymerizable unsaturated compound such as a polymerizable monomer or a polymerizable oligomer is mixed into the molded article as a substitute for the plasticizer of the molded article, and the stretched article is stretched while the stretchability is improved. , Mechanical properties such as tensile strength and elastic modulus are improved. Further, after stretching, the polymerizable unsaturated compound is polymerized, thereby eliminating the need for a conventional removal step. Therefore,
A polyolefin molded body having high productivity and high strength and high elastic modulus can be manufactured. Further, since the polymerizable unsaturated compound is polymerized after stretching, there is no occurrence of a phenomenon of seepage onto the surface of the molded article, that is, a so-called bleeding phenomenon.

Therefore, according to the present invention, the high-density polyolefin, which is considered to be very difficult to be stretched due to very many entanglements of the molecular chains, particularly, the weight-average molecular weight is 200,000 to 200,000.
About 500,000 high-density high-molecular-weight polyolefin can be stretched, and strength and elastic modulus can be significantly improved.

In the present invention, heat treatment may be performed before rolling or stretching the sheet or film. That is, by performing a heat treatment for at least one hour or more at a temperature at which crystals can sufficiently transfer, for example, at a temperature of 70 ° C. to the melting point of the polyethylene resin in the case of a polyethylene resin, the crystallization rate can be increased, It is believed that this reduces the entanglement of the polyethylene molecules. By such heat treatment, stretching performed later can be performed smoothly, and the degree of orientation by stretching can be improved.

[0043]

Examples 1 to 17 and Comparative Examples 1 to 8 Production of raw materials As shown in Tables 1 and 2 below, Examples 1 to 3, 6 to 9 and
In Examples 11 to 17 and Comparative Examples 1 to 4 and 6, high-density polyethylene having a weight-average molecular weight of 3.3 × 10 ⁵ and a melting point of 135 ° C. (manufactured by Mitsubishi Chemical Corporation, grade: HY540, density: 0.9)
Using Example 61 and Comparative Example 5, in Example 4 and Comparative Example 5, a high-density polyethylene having a weight-average molecular weight of 1.5 × 10 ⁵ and a melting point of 136 ° C. (manufactured by Mitsubishi Chemical Corporation, grade: HJ560W, density:
0.964), and in Example 5, high-density polyethylene having a weight average molecular weight of 2.2 × 10 ⁵ and a melting point of 132 ° C. (manufactured by Mitsui Petrochemical Co., grade: 5000SR, density:
0.958), in Example 10 and Comparative Examples 7 and 8, high-density polypropylene having a weight average molecular weight of 1.5 × 10 ⁵ and a melting point of 165 ° C. (manufactured by Mitsubishi Chemical Corporation, grade: MA)
3) was used as a high-density polyolefin.

Further, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triallylimicyanurate or divinylbenzene and a radical generator are added to any one of the above high-density polyolefins so as to have the compounding ratio shown in Table 1. Is melted at a resin temperature of about 180 ° C. using a biaxial kneading extruder (PCM30, manufactured by Ikegai Iron and Steel Co., Ltd.) at a temperature of 180 ° C. and a calendering machine at a roll temperature of 80 ° C.
It was formed into a tape having a width of 60 mm and a thickness of 0.7 mm. The amounts shown in Table 1 were all high-density polyolefin 1
Each blending ratio with respect to 00 parts by weight is shown in parts by weight.

As is clear from Table 1, Example 6
In this example, divinylbenzene, which is a bifunctional compound, was used in place of trimethylolpropane trimethacrylate, which is a trifunctional compound.

In Example 7, benzophenone was not added. This is because polymerization is performed by electron beam irradiation in Example 7 as described later. In Comparative Examples 1, 5, and 7, the above polymerizable unsaturated compound and benzophenone were not blended, and in Comparative Example 6, benzophenone was not blended.

Heat Treatment Step Only in Example 8, the sheet was heat treated before the rolling step. That is, in Example 8, after forming a high-density polyethylene sheet in the same manner as in the method of Example 2, prior to the rolling step, the sheet was placed in a container heated to 130 ° C.
Heat treatment was performed for a time.

Rolling Step As shown in Table 1, using a hot roll heated to 115 ° C. (roll diameter: 6 inches, manufactured by Kodaira Seisakusho Co., Ltd.), except for Example 15 (rolling magnification: 8.9 times). Rolling was performed so that the rolling ratio was about 7 times. In Example 10 and Comparative Examples 7 and 8, the rolling temperature was 145 ° C, and in Example 17, the rolling temperature was 85 ° C.

Stretching process The film was stretched using a hot-air heating roll stretching machine so that the stretching ratio became 1.8 times. Next, stretching was performed at the maximum stretching ratio at which the molded body was not cut. The stretching temperature during stretching is 95 ° C
And The total draw ratios shown in Tables 3 and 4 below are the products of the roll ratio and each draw ratio.

In Example 9, two-stage stretching was performed at different temperatures and magnifications. That is, in the ninth embodiment, the second embodiment
And then stretched 1.8 times at 95 ° C. using a hot-air heating roll stretching machine.
° C and the final stretching step was performed at a stretching ratio of 2.7 times. In Example 10, the stretching temperature in the first and second stages was set to 1
60 ° C.

Polymerization Step Molding after stretching is performed using an apparatus in which three non-electrode UV irradiation lamps (manufactured by Fusion Japan Co., Ltd.) are arranged on each of the front and back sides so that the front and back sides of the molded body can be irradiated. The body was irradiated by passing through at a speed of 10 m / min. Thereby, the polymerizable monomer in the molded body was polymerized.

As shown in Table 2, Comparative Examples 3 and
In Nos. 4 and 8, no ultraviolet light was irradiated. Example 7
Then, instead of the above ultraviolet irradiation, an area beam type electron beam irradiation device (manufactured by Nissin Hivol Large Co., Ltd., trade name: Curetron) was used to irradiate an electron beam at room temperature for 2 seconds with an irradiation amount of 10 MRad. .

The molded product obtained as described above was measured for tensile strength and tensile modulus. The measuring method is as follows. The results are shown in Tables 3 and 4. Tensile Strength and Tensile Modulus A tensile tester (manufactured by Orientic, model: Tensilon) was used in accordance with JIS K7113.
In addition, the test piece was produced using the No. 2 dumbbell. Also,
The surfaces of the test specimens were observed, and those having bleed on the surface were evaluated as “present”, and those without bleed were evaluated as “absent” in Tables 3 and 4.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

Examples 1 to 3 and Comparative Examples 1 and 2 examine the influence of the amount of trimethylolpropane trimethacrylate. As is clear from Tables 1 to 4, all Examples show higher tensile strength and tensile modulus than Comparative Example 1 in which trimethylolpropane trimethacrylate is not blended. Further, as is apparent from the comparison between Example 3 and Comparative Example 2, it is found that the blending amount of trimethylolpropane trimethacrylate has a limit, and when the amount exceeds the limit, the mechanical properties decrease.

Comparative Examples 3 and 4 are the same as Examples 2 and 3 except that UV irradiation was not performed and polymerization was not performed. When no polymerization is performed, as shown in Table 4, it is found that bleeding occurs and mechanical properties are deteriorated. As is clear from the comparison of Examples 4 to 6, it is found that higher strength and elastic modulus can be obtained by using polyethylene having a higher molecular weight.

As is clear from the results of Example 6, when divinylbenzene, which is a bifunctional compound, is used as a polymerizable unsaturated compound, a considerable amount of trimethylolpropane triacrylate, which is a trifunctional compound, is used. Compared with Example 2, although the strength and the elastic modulus are the same,
Due to the poor reactivity of divinylbenzene, some bleed was observed on the sheet surface. However, even in the high-density polyethylene sheet obtained in Example 6, Comparative Examples 1 to 4
It can be seen that the sheet shows sufficient strength and elastic modulus as compared with the high-density polyethylene sheet obtained in the above.

Further, in Example 7, trimethylolpropane triacrylate was polymerized by electron beam irradiation without using benzophenone. In this case, too, stiffness and elasticity were sufficient, and bleeding was observed on the surface. It can be seen that no high density polyethylene sheet is obtained.

In Example 8, the heat treatment described above in the method of Example 2 was performed prior to rolling, but the high-density polyethylene sheet obtained in Example 8 was obtained by performing the heat treatment described above. It can be seen that the strength and elastic modulus can be further increased as compared with the high-density polyethylene sheet.

In Example 9, as described above, multi-stage stretching was performed and the stretching temperature in the final stretching step was lowered.
In the obtained high-density polyethylene sheet, the total stretching ratio was as high as 34.1 times, many fine voids were generated, and the sheet was whitened. The specific gravity of the high-density polyethylene sheet obtained in Example 2 was 0.95, while the specific gravity of the high-density polyethylene sheet obtained in Example 9 was 0.85. It turns out that it gets.

In Example 10, the above-mentioned high-density polypropylene having a weight-average molecular weight of 1.5 × 10 ⁵ and a melting point of 165 ° C. was used, the rolling temperature was 145 ° C., and the stretching temperature was 160 ° C. As is clear from Table 3 and Table 4 in which the physical property values of Comparative Examples 7 and 8 using the same high-density polypropylene are described, high-density polypropylene having sufficient strength and elastic modulus and having no bleed on the surface is observed. It can be seen that a sheet can be obtained.

On the other hand, Comparative Example 6 was the same as Example 2 except that benzophenone was not blended in Example 2, except that no radical source was present. Also, trimethylolpropane trimethacrylate did not polymerize and bleed-out was observed in the stretched sheet.

[0066]

As described above, according to the present invention, a polyolefin molded article having a high strength and a high modulus of elasticity can be efficiently produced without the need for a step of removing a fluidity improver. can do.

According to the second aspect of the present invention, since a high-molecular-weight polyolefin is used as the high-density polyolefin, a polyolefin molded article having higher strength and a higher elastic modulus can be efficiently produced.

According to the third aspect of the invention, since the composition further contains a radical generator, the radical generator is activated to easily polymerize the polymerizable unsaturated compound. Thus, a polyolefin molded article having high strength and high elastic modulus can be efficiently obtained without requiring a step of removing a polymerizable unsaturated compound.

According to the fourth aspect of the present invention, since the radical generator is a photopolymerization initiator and the step of polymerizing the polymerizable unsaturated compound after stretching is performed by ultraviolet irradiation, mechanical shrinkage due to heat or mechanical stretching due to stretching is performed. The physical properties are not easily reduced, and the photopolymerization initiator is activated by irradiation with ultraviolet rays, so that the polymerizable unsaturated compound can be easily and reliably polymerized using inexpensive equipment.

According to the fifth aspect of the present invention, since the polymerizable unsaturated compound can be polymerized by electron beam irradiation, the mechanical properties such as strength and elastic modulus are hardly reduced due to shrinkage due to heat and mechanical properties due to stretching. Thus, a polyolefin molded article having excellent physical properties can be reliably obtained.

In the invention according to claim 6, since a highly reactive trifunctional compound is used as the polymerizable unsaturated compound, the polymer of the polymerizable unsaturated compound hardly bleeds on the surface of the polyolefin molded article.

According to the seventh aspect of the present invention, since the rolling is performed at a rolling ratio of 2 to 10 at the time of rolling, the load of the stretching step performed later can be reduced.
Uniform rolling can be performed, and cutting of the formed body in a stretching step performed later can be prevented.

In the invention according to claim 8, when stretching,
Since the stretching is performed at a stretching ratio of 2 or more, a polyolefin molded article having excellent strength and elastic modulus can be obtained, and the molded article during the stretching is hardly cut.

According to the ninth aspect of the present invention, since high-density high-molecular-weight polyethylene having a weight average molecular weight in the range of 200,000 to 500,000 is used as the high-density polyolefin resin, the strength and the elastic modulus are further improved. A polyolefin molded article can be obtained.

According to the tenth aspect of the present invention, in the rolling step, since the rolling is performed in a temperature range of 70 to 120 ° C.,
Uniform rolling can be performed by using an appropriate rolling force, and the polyolefin molded body during rolling is hardly melted.

According to the eleventh aspect of the present invention, in the stretching step, the stretching is performed in a temperature range from 70 ° C. to the melting point of the high-density polyethylene. The molded article is less likely to be stretched, and the effect of improving the strength by stretching can be stably obtained.

According to the twelfth aspect of the present invention, since the sheet or film is heat-treated at least before stretching, the crystalline state of the sheet or film is adjusted, and the effect of improving the degree of orientation by stretching performed later can be enhanced. Stretching can be performed more smoothly.

According to the thirteenth aspect, in performing the multi-stage stretching, the stretching temperature is set to be lower than the stretching temperature immediately before the final stretching step by three times.
In order to carry out the final stretching step of stretching in the same direction at a temperature of 5 ° C. or lower and at a temperature of 5 ° C. or lower than the stretching temperature, fine voids can be stably generated in the polyolefin molded body in the final stretching step. It is possible to reduce the weight of the polyolefin molded article.

Claims (13)

[Claims] 1. 100 parts by weight of a high-density polyolefin,
A step of melting a composition containing 1 to 30 parts by weight of a polymerizable unsaturated compound having an affinity for the high-density polyolefin as a main component, and forming the sheet or film; and a step of rolling the sheet or film. A method for producing a polyolefin molded body, comprising: a step of stretching the rolled sheet or film; and a step of polymerizing the polymerizable unsaturated compound in the stretched sheet or film. 2. The method according to claim 1, wherein the high-density polyolefin is a high-molecular-weight polyolefin. 3. The method for producing a polyolefin molded product according to claim 1, wherein the composition further contains a radical generator. 4. The process for producing a polyolefin molded article according to claim 3, wherein the radical generator is a photopolymerization initiator, and the step of polymerizing the polymerizable unsaturated compound after stretching is performed by ultraviolet irradiation. Method. 5. The method according to claim 1, wherein the step of polymerizing the polymerizable unsaturated compound is performed by electron beam irradiation.
Or the method for producing a polyolefin molded article according to 2. 6. The polymerizable unsaturated compound according to claim 1, wherein at least a part of the polymerizable unsaturated compound is a trifunctional compound.
The method for producing a polyolefin molded article according to any one of the above. 7. The method for producing a polyolefin molded product according to claim 1, wherein in the step of rolling the sheet or film, the sheet or film is rolled to a rolling ratio of 2 to 10 times. 8. The method for producing a polyolefin molded article according to claim 1, wherein in the step of stretching the sheet or film, the sheet or film is stretched to a stretching magnification of 2 times or more. 9. The polyolefin molding according to claim 1, wherein the high-density polyolefin is high-density polyethylene and has a weight average molecular weight in a range of 200,000 to 500,000. How to make the body. 10. In the rolling step, 70 to 120
The method for producing a polyolefin molded article according to claim 9, wherein the rolling is performed in a temperature range of ° C. 11. The method for producing a polyolefin molded product according to claim 9, wherein the stretching is performed in a temperature range from 70 ° C. to a melting point of the high-density polyethylene. 12. The method for producing a polyolefin molded product according to claim 1, further comprising a step of heat-treating the sheet or film at least before stretching. 13. The stretching step comprises a multi-stage stretching step of stretching two or more times in the same direction as the rolling direction, wherein the stretching temperature in the stretching step immediately before the final stretching step is 35 ° C.
The method for producing a polyolefin molded article according to any one of claims 1 to 12, further comprising a final stretching step of stretching in the same direction at a temperature equal to or lower than a low temperature and equal to or lower than a temperature lower by 5 ° C than the stretching temperature.